1. Field of the Invention
The present invention relates to radiation detection, and, more specifically, to the detection of ionizing radiation using large area silicon solid state detectors.
2. Description of Related Art including information disclosed under 37 CFR 1.97 and 1.98
Silicon Drift Detectors (SDD) having concentric drift electrodes around an anode on the counter irradiation side and a continuous p+ junction on the irradiation side are known in the art. FIG. 1 depicts such a traditional SDD having such circular anode. The benefit of a small anode is that it reduces the detector capacitance. This lower capacitance reduces the series-noise component and thus reduces the overall inherent electronic noise of the device. Thus, because of their low capacitance, such SDDs have been known to have superior noise features when compared to pin diodes. However, very large area SDDs (i.e., >100 mm2) face other significant limitations.
One such limitation is the ballistic deficit. The ballistic deficit causes free electrons generated from the radiation absorption within the material to repel each other as they drift towards the anode. This repulsion results in a pronounced spread between the drifting electrons. This spread does not allow all electrons to reach the anode at the same time. Consequently, larger shaping times must be utilized by the detection circuitry which further limits the practical size of the SDDs. A larger shaping time also reduces count rate performance due to the influence of leakage current.
To improve count rate performance, others have developed very small area pin pixel devices that couple each pixel to an electronic channel. However, this approach requires the use of specialized interconnects and flip chip techniques and does not meet the required resolution for many radiation detection applications.